Previous Screening Mammograms Research Articles

Interval breast cancer: radiological surveillance in screening Egyptian population

BackgroundInterval cancers might be divided into true negative interval cancer where a new lesion is detected that no sign of disease could be detected on previous screening mammogram. For false-negative interval cancers, those missed for overt symptoms and those missed for mild or undetectable ones, this includes interpretive error as benign interval cancer (benign mimics), subtle changes, masked carcinoma or slowly growing or patient factors, such as the dense breast parenchyma. Technical failure interval cancer hampered the reader to discover the abnormality. The aim of this study was to relate the risk factors for the development of the interval breast cancer such as breast density, positive family history of breast cancer in Egyptian population. Highlight the causes of missed breast cancer in order to overcome it in the future radiological interpretation.MethodsA total of 74,546 screening mammographic examinations were performed in the radiology department at specialized breast cancer center in the period between 2015 and 2021 with about 844 pathologically proved malignant cases. Out of the 844 pathologically proven breast cancer cases, 185 breast cancer patients were interval breast cancer having reported normal examination in the previous year, 88 were true interval breast cancer and 97 were missed on mammography and detected later on. The cases were subjected to full-field digital mammogram (FFDM), complementary ultrasound, contrast-enhanced digital mammography (CEDM) and magnetic resonance imaging (MRI) in some cases, and all cases were histopathologically proven by either fine needle aspiration, core needle biopsy (CNB) or open biopsy.ResultsThe mean age of the patients was 53.5 years (range 36–83 years). The overall breast cancer detection rate was 11 per 1000 women. The 185 interval cancers were present at a rate of 3.8 per 1000 women. True negative interval breast cancers where 88 cancers were not present in retrospect on screening mammograms, 17 cases present with benign findings (benign mimics mass or calcifications) and 80 cancers were missed cancers. Analysis of the cause of missed carcinoma revealed patient-related, tumor-related, or provider-related factors. Tumor factors were the most commonly encountered, accounting for 49.5% (48 cases), then provider factors in 25.8% (25 cases) while the patient factors were the least commonly encountered in 24.7% (24 cases). Recorded positive family history found in about 35% (31cases) of the true interval breast cancers.ConclusionsAlthough mammography is the standard for detecting early breast cancer, some cancers can be missed due to various causes. Mammographic interpretation must meet high standards to reduce missed cancers. Radiologists should carefully assess screening views and order additional imaging if needed. Palpable lesions and clinical data should be further examined with ultrasound and contrast imaging if necessary. Always compare current images with previous examinations to check for any changes in lesion size. When one pathology is found, search for additional lesions.

Signed family physician reminder letters to women overdue for screening mammography: A randomized clinical trial.

To determine whether signed family physician reminder letters to women overdue for screening mammography prompts rescreening. A randomized double-blind trial conducted in 2013 among women aged 51-73 and overdue for screening by 6-24 months. The study was carried out by the publicly funded British Columbia Cancer Agency Screening Mammography Program, which routinely sends standard reminder postcards to women who are due for mammography. Participating family physicians signed letters for the overdue women in their practices. The overdue women were mailed either the signed reminder letter and the standard reminder postcard, or the standard reminder postcard alone. The primary endpoint was the proportion of overdue women that attended a screening mammogram appointment within six months of mailing the study letters. The analysis was by intention to treat. In total, 822 family physicians participated and 5638 women were randomized. Mammography attendance by six months after mailing the reminders was 34.4% (947/2749) for women in the signed family physician letter arm, compared with 24.0% (660/2749) for women in the control arm (p < 0.0001). Adjusting for age, number of previous screening mammograms, and months overdue, women in the signed letter arm were significantly more likely to return for screening than women in the control arm (RR 1.41; 95% confidence interval: 1.30-1.54). A signed family physician reminder letter improved mammography attendance for women who were overdue for screening mammography.

Local breast density at lesion sites in diagnostic and previous screening mammograms

High overall breast density is associated with increased risk of developing cancer. Semi-automated analysis of digitised analogue mammograms has previously suggested that local increases in density may occur prior to cancers being detected. We investigate local density at the site of cancers in diagnostic and previous full-field digital screening mammograms using quantitative measures.

PB.23. Breast density in previous screening mammograms of women with and without breast cancer

Increased mammographic density is a well-established risk factor for breast cancer; much of the evidence is based on semi-automated or visual assessment of analogue mammograms, although volumetric measures from digitally acquired mammograms are now being reported. It is also possible to quantify volumes of fat and gland from digitised analogue mammograms, given suitable calibration data. We have measured breast density in cancer cases and controls which had previous analogue screening mammograms in the PROCAS (Predicting Risk Of Cancer At Screening) study.

Trends in incidence and detection of advanced breast cancer at biennial screening mammography in The Netherlands: a population based study

IntroductionThe aims of this study were to determine trends in the incidence of advanced breast cancer at screening mammography and the potential of screening to reduce it.MethodsWe included a consecutive series of 351,009 screening mammograms of 85,274 women aged 50-75 years, who underwent biennial screening at a Dutch breast screening region in the period 1997-2008. Two screening radiologists reviewed the screening mammograms of all advanced screen detected and advanced interval cancers and determined whether the advanced cancer (tumor > 20 mm and/or lymph node positive tumor) had been visible at a previous screen. Interval cancers were breast cancers diagnosed in women after a negative screening examination (defined as no recommendation for referral) and before any subsequent screen. Patient and tumor characteristics were compared between women with advanced cancer and women with non-advanced cancer, including ductal carcinoma in situ.ResultsA total of 1,771 screen detected cancers and 669 interval cancers were diagnosed in 2,440 women. Rates of advanced cancer remained stable over the 12-year period; the incidence of advanced screen-detected cancers fluctuated between 1.5 - 1.9 per 1,000 screened women (mean 1.6 per 1,000) and of advanced interval cancers between 0.8 - 1.6 per 1,000 screened women (mean 1.2 per 1,000). Of the 570 advanced screen-detected cancers, 106 (18.6%) were detected at initial screening; 265 (46.5%) cancers detected at subsequent screening had been radiologically occult at the previous screening mammogram, 88 (15.4%) had shown a minimal sign, and 111 (19.5%) had been missed. Corresponding figures for advanced interval cancers were 50.9% (216/424), 24.3% (103/424) and 25.1% (105/424), respectively. At multivariate analysis, women with a ≥ 30 months interval between the latest two screens had an increased risk of screen-detected advanced breast cancer (OR 1.63, 95%CI: 1.07-2.48) and hormone replacement therapy increased the risk of advanced disease among interval cancers (OR 3.04, 95%CI: 1.22-7.53).ConclusionWe observed no decline in the risk of advanced breast cancer during 12 years of biennial screening mammography. The majority of these cancers could not have been prevented through earlier detection at screening.

634 Uptake of mammography screening in women aged over 75

The aim of this study was to examine how frequently the later-round screen-detected and interval breast cancers were visible in earlier screening mammograms by retrospective review and to compare their radiological and clinicopathological features with those diagnosed by primary screening. In a population-based mammography screening programme 63 731 women aged 50–59 years were invited and 56 158 examinations were carried out in the period 1987–1992 in the Tampere area in Finland. A total of 276 breast cancers were detected, of which 131 were diagnosed on later screening rounds or were interval cancers. A retrospective review of previous screening mammograms was carried out in 130 cases by the radiologist who diagnosed the breast cancer and thus knew the exact location of the tumour, no blinded review was carried out. 43 (33%) cancers were visible, 84 (65%) were not visible and 3 (2%) not included on the mammogram in a retrospective review. Later round screen-detected cancers were statistically significantly more often visible in earlier screening mammograms (43%) than interval cancers (19%) (P=0.002). Tumours missed by screening mammography but which were visible on retrospective review were often histologically well-differentiated and were more often diagnosed in the subsequent screening round than by clinical diagnosis as interval cancers. If all retrospectively visible interval cancers had been diagnosed by screening 19% (10/54) of the interval cancers could have been avoided. If all retrospectively visible cancers had been diagnosed at the time of false-negative screening or assessment 65% (84/130) of all patients would have benefitted from an earlier diagnosis compared with the actual figure of 31% (41/130).

An Automated Approach for Estimation of Breast Density

Breast density is a strong risk factor for breast cancer; however, no standard assessment method exists. An automated breast density method was modified and compared with a semi-automated, user-assisted thresholding method (Cumulus method) and the Breast Imaging Reporting and Data System four-category tissue composition measure for their ability to predict future breast cancer risk. The three estimation methods were evaluated in a matched breast cancer case-control (n = 372 and n = 713, respectively) study at the Mayo Clinic using digitized film mammograms. Mammograms from the craniocaudal view of the noncancerous breast were acquired on average 7 years before diagnosis. Two controls with no previous history of breast cancer from the screening practice were matched to each case on age, number of previous screening mammograms, final screening exam date, menopausal status at this date, interval between earliest and latest available mammograms, and residence. Both Pearson linear correlation (R) and Spearman rank correlation (r) coefficients were used for comparing the three methods as appropriate. Conditional logistic regression was used to estimate the risk for breast cancer (odds ratios and 95% confidence intervals) associated with the quartiles of percent breast density (automated breast density method, Cumulus method) or Breast Imaging Reporting and Data System categories. The area under the receiver operator characteristic curve was estimated and used to compare the discriminatory capabilities of each approach. The continuous measures (automated breast density method and Cumulus method) were highly correlated with each other (R = 0.70) but less with Breast Imaging Reporting and Data System (r = 0.49 for automated breast density method and r = 0.57 for Cumulus method). Risk estimates associated with the lowest to highest quartiles of automated breast density method were greater in magnitude [odds ratios: 1.0 (reference), 2.3, 3.0, 5.2; P trend < 0.001] than the corresponding quartiles for the Cumulus method [odds ratios: 1.0 (reference), 1.7, 2.1, and 3.8; P trend < 0.001] and Breast Imaging Reporting and Data System [odds ratios: 1.0 (reference), 1.6, 1.5, 2.6; P trend < 0.001] method. However, all methods similarly discriminated between case and control status; areas under the receiver operator characteristic curve were 0.64, 0.63, and 0.61 for automated breast density method, Cumulus method, and Breast Imaging Reporting and Data System, respectively. The automated breast density method is a viable option for quantitatively assessing breast density from digitized film mammograms.

Breast Imaging and Computer-Aided Detection

Breast imaging is the newest, and according to most criteria the weakest, of all radiology subspecialties. Screening mammography in particular often loses money and is subsidized by other sections of the radiology department and occasionally, as in my own case, by direct hospital payments to breast imagers. Screening mammography is also the most common basis for lawsuits in radiology, which is not surprising, since 25 to 50% of cases of breast cancer are identified retrospectively on the previous annual screening mammogram. As the only quasi–public health endeavor in radiology, screening mammography is heavily regulated, with many unfunded mandates. Screening mammography, . . .

Cost-effectiveness of different reading and referral strategies in mammography screening in the Netherlands

In mammography screening with double reading, different strategies can be used when the readers give discordant recommendations for referral. We investigated whether the results of the Dutch breast cancer screening programme can be optimised by replacing the standard referral strategy by consensus. Twenty-six screening radiologists independently and blinded to outcome read a test set consisting of previous screening mammograms of 250 cases (screen-detected and interval cancers) and 250 controls. Their referral recommendations were paired and, in case of discrepancy, re-read according to three referral strategies: (1) decision by one of the readers; (2) arbitration by a third reader; (3) referral if both readers agree (consensus). Data allowed studying other referral strategies, including referral if any reader suggests, as well. Double reading with referral if any reader suggests resulted in a 1.03 times higher sensitivity (76.6%) and a 1.31 times higher referral rate (1.26%) than double reading with consensus. To estimate the cost-effectiveness, the outcomes were used in a microsimulation model. Even if double reading with referral if any reader suggests results in four times as high referral rates and an accompanying increase of biopsies or other invasive procedures, the cost-effectiveness of 4,190 Euros per life-year gained may well be in the range of acceptable cost-effectiveness for Dutch health care programmes.

Routine mammograms in symptomatic women

The aim of this study was to examine how frequently the later-round screen-detected and interval breast cancers were visible in earlier screening mammograms by retrospective review and to compare their radiological and clinicopathological features with those diagnosed by primary screening. In a population-based mammography screening programme 63 731 women aged 50–59 years were invited and 56 158 examinations were carried out in the period 1987–1992 in the Tampere area in Finland. A total of 276 breast cancers were detected, of which 131 were diagnosed on later screening rounds or were interval cancers. A retrospective review of previous screening mammograms was carried out in 130 cases by the radiologist who diagnosed the breast cancer and thus knew the exact location of the tumour, no blinded review was carried out. 43 (33%) cancers were visible, 84 (65%) were not visible and 3 (2%) not included on the mammogram in a retrospective review. Later round screen-detected cancers were statistically significantly more often visible in earlier screening mammograms (43%) than interval cancers (19%) (P=0.002). Tumours missed by screening mammography but which were visible on retrospective review were often histologically well-differentiated and were more often diagnosed in the subsequent screening round than by clinical diagnosis as interval cancers. If all retrospectively visible interval cancers had been diagnosed by screening 19% (10/54) of the interval cancers could have been avoided. If all retrospectively visible cancers had been diagnosed at the time of false-negative screening or assessment 65% (84/130) of all patients would have benefitted from an earlier diagnosis compared with the actual figure of 31% (41/130).

Breast cancer screening in the Netherlands: audit and training of radiologists

The National Expert and Training Centre has for the past 15 years been in charge of medical and technical quality control in the Dutch population-based screening program. Audit is an important tool for keeping up with and improving quality standards. Between 1994 and 2002, we visited most of the 28 central units of the screening program twice, making over 50 audits in total. During audits, we reviewed interval cancers and Stage II screen-detected cancers. Referral rates for subsequent exams varied from 0.43% to 1% in the first series and had increased to 0.6% to 1.6% in the next audits. This led to higher detection rates (first series 2.4–4.0/1,000; second series 3.6–4.7/1,000). For women aged 50 to 69 years, detection rate in subsequent screening exams was 3.9 per 1,000 in 1999. Review of interval cancers showed fewer cases with tumor signs retrospectively visible on the previous screening mammograms (first series 54%, second series 44%). Because of the small numbers of reviewed cases (usually 80 interval- and 40 screen-detected cancers), resulting figures have relatively wide confidence intervals. Presentation of audit results in scatter diagrams can aid comparison with other central units. In most central units, over 80% of screen-detected malignancies are T1 invasive tumors or ductal carcinoma in situ. In 70% of screen-detected invasive cancers, axillary lymph nodes were negative. Results are generally in agreement with expectations stated at the start of the program.

Use of previous screening mammograms to identify features indicating cases that would have a possible gain in prognosis following earlier detection

False-negative screening mammograms generally refer to breast cancers that were overlooked or misinterpreted at screening. An important question is whether earlier detection could have made a difference in the prognosis of the women concerned. We reviewed screening and diagnostic mammograms of 234 screen-detected and interval cancer cases (aged 44–84 years) diagnosed between 1991 and 1996 in the Nijmegen breast cancer screening programme. A lesion was visible on 117 (50%) of the screening mammograms prior to the diagnosis of breast cancer. Fifty-one out of the 117 cancers had poor prognostic characteristics at diagnosis (i.e. N+ and/or T2+) and could potentially have benefited from an earlier diagnosis (‘possible gain’). The ‘possible gain’ cases were more often characterised by architectural distortion (29 vs. 10%; P=0.01) or a high-density mass (25 vs. 13%; P=0.06) on the mammogram prior to diagnosis than the 58 ‘no gain’ cases. Our study shows that architectural distortion and non-spiculated high-density masses on the mammogram prior to diagnosis are associated with a possible gain in prognosis. Earlier detection of the carcinomas preceded by these signs may well have an impact on breast cancer mortality and thus warrant extra attention in radiological practice.

An unusual case of an enlarging mass on a screening mammogram: a case report and review of the radiology and current literature

We report the case of a woman who was recalled after screening because an opacity seen on her previous screening mammogram had changed in appearance. The new features were of a circumscribed soft-tissue opacity with some lobulation. Ultrasound showed an oval mass which was slightly hypoechoic compared to the surrounding fatty parenchyma and contained small focal anechoic areas. The lesion was biopsied and found to be a cavernous haemangioma. Haemangioma of the breast is a rare cause of a well-circumscribed soft-tissue mass on a mammogram.

The pattern of breast cancer screening utilization and its consequences.

The objective of this study was to describe the pattern of screening utilization and its consequences in terms of tumor size and time of tumor appearance of invasive breast carcinoma among a population of women who were examined at a large service screening/diagnostic program over the last decade. Utilization of mammography was assessed from a population of 59,899 women who received 196,891 mammograms at the Massachusetts General Hospital Breast Imaging Division from January 1, 1990 to March 1, 1999, among which 604 invasive breast tumors were found. Two hundred six invasive, clinically detected tumors also were seen during this period among women who had no record of a previous mammogram. Additional information was available on screening of women from March 1, 1999 to June 1, 2001. Fifty percent of the women who used screening did not begin until the age of 50 years, although 25% of the invasive breast tumors were found in women age < 50 years. Relatively few of the women who used screening returned promptly for their annual examinations; by 1.5 years, only 50% had returned. Approximately 25% of the invasive breast tumors were found in women for whom there was no record of a previous screening mammogram, and these tumors were larger (median, 15 mm) than the screen-detected tumors (median, 10 mm). Approximately 30% of the 604 invasive breast tumors in the screening population were found on nonmammographic grounds, and they also were larger (median, 15 mm) than the screen-detected tumors (median, 10 mm). However, only 3% of these 604 tumors were found by nonmammographic criteria within 6 months of the previous negative examination, and only 12% were found within 1 year. By back calculating the likely size of each of these tumors at the time of the negative mammogram, it could be seen that most tumors probably emerged as larger, palpable masses not because they were missed at the previous negative mammogram, because most were too small then to have been detected, but because too much time had been allowed to pass. Far too many women did not comply with the American Cancer Society recommendation of prompt annual screening from the age of 40 years. Consequently, almost 50% of the invasive tumors emerged as larger and, thus, potentially more lethal, palpable masses.

Radiological review of incidence breast cancers

To examine the rate of incidence cancers detectable on review of previous screening mammograms using two reviewing methods. To compare the results with a previous study of interval cancers using the same reviewing methods. Almost 50000 women are regularly invited for service screening at Stockholm Söder Hospital. From 1989 to 1993, 119 women were identified with breast cancer detected at screening and the previous round attendance (incidence cancer). Screening mammograms, obtained before detection of the incidence cancers, were reviewed first mixed with other screening images (ratio 1:8) and then non-mixed. Reviewers from the screening unit responsible for the mammograms as well as reviewers from other units interpreted all images by both single and double reading. The proportion detected on retrospective review varied between 5% and 50% depending on the review method used and the number of reviewers included to classify a case as truly identified. Generally more cancers were detected when non-mixed samples of mammograms were reviewed than when mixed samples were reviewed (mean increase 23%) and when interpreted by double reading compared with single reading (mean increase 14%). In an experimental retrospective set up, fewer incidence cancers were identified in mixed than in non-mixed review. Generally more incidence cancers were identified on review (22%) than previously reported for interval cancers (14%), probably reflecting differences in tumour biology and growth. How many women with potentially visible incidence cancers would have benefited from earlier tumour detection still needs to be evaluated.

A blind review and an informed review of interval breast cancer cases in the Limburg screening programme, the Netherlands.

To investigate the proportion of interval breast cancers that could have been detected at the previous screening examination, and to gain more insight into the characteristics of these tumours. Breast cancer screening programme in mid- and southern Limburg, the Netherlands. Firstly, previous screening mammograms of 92 interval cancer cases were blindly reread by the radiologists from two different units as part of their daily screening workload. Secondly, a separate informed review was conducted, in which all of the cases (except for two) were subclassified into four categories: screening error; minimal signs; radiologically occult both at previous screening and at diagnosis; or radiologically occult at previous screening. Trends in recall rates and false and true positive rates were calculated to study potential changes during and after the blind review. In the blind review, 15% of the interval cancers were detected in both rereadings and 21% in one rereading. In the informed review, 25% were classified as a screening error and 24% as minimal signs present; 74% of the cases classified as a screening error had been recalled at least once in the blind review. Recall rates and false positive rates in daily screening practice increased significantly during and after the study period. About one third of the interval cancers could have been detected in the previous screening round. In order to diminish the number of avoidable interval cancers, review and classification of interval cancers is an important tool for continuing the education of screening radiologists. Therefore, further development of review training procedures is necessary.

The visibility of cancer on earlier mammograms in a population-based screening programme

The aim of this study was to examine how frequently the later-round screen-detected and interval breast cancers were visible in earlier screening mammograms by retrospective review and to compare their radiological and clinicopathological features with those diagnosed by primary screening. In a population-based mammography screening programme 63 731 women aged 50–59 years were invited and 56 158 examinations were carried out in the period 1987–1992 in the Tampere area in Finland. A total of 276 breast cancers were detected, of which 131 were diagnosed on later screening rounds or were interval cancers. A retrospective review of previous screening mammograms was carried out in 130 cases by the radiologist who diagnosed the breast cancer and thus knew the exact location of the tumour, no blinded review was carried out. 43 (33%) cancers were visible, 84 (65%) were not visible and 3 (2%) not included on the mammogram in a retrospective review. Later round screen-detected cancers were statistically significantly more often visible in earlier screening mammograms (43%) than interval cancers (19%) ( P=0.002). Tumours missed by screening mammography but which were visible on retrospective review were often histologically well-differentiated and were more often diagnosed in the subsequent screening round than by clinical diagnosis as interval cancers. If all retrospectively visible interval cancers had been diagnosed by screening 19% (10/54) of the interval cancers could have been avoided. If all retrospectively visible cancers had been diagnosed at the time of false-negative screening or assessment 65% (84/130) of all patients would have benefitted from an earlier diagnosis compared with the actual figure of 31% (41/130).

Second round cancers: How many were visible on the first round of the UK national breast screening programme, three years earlier?

The first round screening films of 100 women who had cancers detected in the second round of the NHS Breast Screening Programme, were reviewed blindly, and then retrospectively, with knowledge of the site of the subsequent cancer. On initial blind viewing of the first screening mammograms, a lesion, later histologically proven to be the cancer, was correctly identified in 25 false-negative lesions. However, 51 false positive lesions which did not develop into cancer were also identified. Review with knowledge of the site of the lesions at second round screening identified an additional 19 false negative lesions. The mammographic features of the 25 false negative lesions initially identified on blind review were ill-defined masses (52%), architectural distortion (20%), asymmetrical densities (16%), enlarged lymph nodes (8%) and a well defined lesion (4%). Sixteen of these lesions were classified as minimal change, suspicious change in four, clearly malignant in three and benign in two. Forty-eight percent of the false negative lesions occurred in the established review areas of the breast. On retrospective review, 25% of incident round screen detected breast cancers were potentially detectable on the previous screening mammograms and the majority of these lesions were ill-defined masses that were more likely to occur in the 'review areas' of the breast. However, only 7% demonstrated mammographic features that were clearly recognized as suspicious of malignancy. We therefore recommend that radiologists involved in screen reading should pay particular attention to abnormalities occurring in the so-called review areas.

Predictors of attendance at a relocatable mammography service for rural women.

This study aimed to identify factors that predicted attendance at a relocatable screening mammography service in a rural centre in Victoria. A cohort design was used whereby 180 women from the target population were interviewed by telephone two weeks before the service moved to the area for a 10-week period of operation. Attendance data were ascertained from service records. Fifty per cent of the sample attended the service. Significant predictors of attendance were: mammographic history, with women who reported previous screening mammography being less likely to attend than women who had not had a previous mammogram (odds ratio (OR) 0.38, 95% confidence interval (CI) 0.17 to 0.83); perception of personal risk for breast cancer, with women who perceived at least some risk being more likely to attend than women who perceived no risk (OR 2.73, CI 1.07 to 6.99); stated intention of attending (OR 2.01, CI 1.49 to 2.71); knowing the correct location of the service (OR 3.08, CI 1.37 to 6.89); and education, with higher education being associated with a lower likelihood of attending (OR 0.65, CI 0.44 to 0.96). Our study raised some issues, including the high prevalence of rural women who reported a previous screening mammogram, although BreastScreen services had not previously been available in their area; factors underlying perceptions of personal risk for breast cancer; and the generalisability of our finding of an inverse relationship between higher education and attendance for screening.

The current detectability of breast cancer in a mammographic screening program. A review of the previous mammograms of interval and screen-detected cancers.

The occurrence of an interval cancer in a mammographic screening program is indicative of a suboptimum effect on mortality, because the very aim of the screening is to detect as many cancers as possible and at their earliest possible stage. In several studies, the previous screening mammograms of patients with an interval cancer were reviewed and the reasons for the "missed diagnosis" were classified into four categories: "screening error" (20-29%), "minimal sign present" (30-40%), "radiographically occult" (33-58%), or "radiographically occult at diagnosis" (occult both at previous screening and diagnosis; 7-16%). A similar procedure was followed in the Nijmegen screening project with patients recently diagnosed as having interval cancer or screen-detected cancer. The previous screening mammograms of 40 interval and 44 screen-detected cases from the breast cancer screening program in Nijmegen were reviewed and categorized as specified above. These breast cancers were diagnosed clinically before the patient was invited to the eighth screening round (interval cancer) or were detected at the eighth screening round (screen-detected cancer). All these patients had been screened in the seventh round (1987-88). Thirteen percent of all cases were classified as "screening error," 38% as "minimal sign present," 43% as "radiographically occult," and 6% as "radiographically occult at diagnosis." In nearly half of the screen-detected cancers, minimal signs appeared to be present on the previous screening mammogram 2 years before the diagnosis. Annual instead of biennial screening may advance detection in most of the "screening error" cases as well as in some in the categories "minimal sign present" and "radiographically occult" at the previous screening. Meticulous analysis of the radiologic characteristics of the "minimal sign present" cases may very well lead to results showing that earlier detection is possible without a significant decrease in the specificity of the screening test.